add with_locale variety utf8 case mapping functions

Submitted by Eric Albright

I need g_utf8_strup_with_locale and g_utf8_strdown_with_locale.

Looks to me like this functionality was planned but not implemented:

http://mail.gnome.org/archives/gtk-i18n-list/2001-June/msg00053.html states "Since we don't have a method of representing locale in GLib right now, I think we should start out with:

g_utf8_toupper (string); [ priority A ] g_utf8_tolower (string); [ priority A ]

Defined to use the "current" locale as the minimum. We can add g_utf8_to_upper_with_locale (string, locale) later."

I don't see why locale cannot be const char * as would be returned by setlocale (LC_CTYPE, NULL) or g_win32_getlocale()

Version: 2.14.x